The seminal discovery by Kohler and Milstein (Kohler, G. and Milstein, C., 1975) of mouse "hybridomas" capable of secreting specific monoclonal antibodies (mAbs) against predefined antigens ushered in a new era in experimental immunology. Many problems associated with antisera were circumvented. Clonal selection and immortality of hybridoma cell lines assured monoclonality and permanent availability of antibody products. At the clinical level, however, the use of such antibodies is clearly limited by the fact that they are foreign proteins and act as antigens to humans.
Since the report of Kohler and Milstein (Kohler, G. and Milstein, C., 1975), the production of mouse monoclonal antibodies has become routine. However, the application of xenogenic mAbs for in vivo diagnostics and therapy is often associated with undesirable effects such as a human anti-mouse immunoglobulin response. mAbs have great potential as tools for imaging; therapeutic treatment has motivated the search into the means of production of human mAbs (humAbs) (Levy, R., and Miller R A., 1983). However, progress in this area has been hampered by the absence of human myelomas suitable as fusion partners with the characteristics similar to those of mouse myeloma cells (Posner M R, et al., 1983). The use of Epstein-Barr virus (EBV) has proved to be quite efficient for human lymphocyte immortalization (Kozbor D, and Roder J., 1981; Casual O, 1986), but has certain limitations such as low antibody secretion rate, poor clonogenicity of antibody-secreting lines and chromosomal instability requiring frequent subcloning. Undifferentiated human lymphoblastoid cell lines appear more attractive. In contrast to differentiated myeloma cells, these cell lines are readily adapted to culture conditions, though the problems of low yield and unstable secretion remain unresolved (Glassy M C, 1983; Ollson L, et al., 1983). The best potential fusion partners are syngenic myeloma cells with well-developed protein synthesis machinery (Nilsson K. and Ponten J., 1975). However, culturing difficulties explain why few lines have been conditioned for in vitro growth and capability to produce viable hybrids (Goldman-Leikin R E, 1989). Existing myelomas have low fusion yield and slow hybrid growth, although mAb production is relatively stable (Brodin T, 1983). Genetic instability is a major disadvantage of interspecies hybrids. This is the case, for example, when a mouse myeloma is used as the immortalizing partner. Production of mouse-human cell hybrids is not difficult. In vitro these cells have growth characteristics similar to those of conventional mouse-mouse hybridomas (Teng N N H, 1983). However, spontaneous elimination of human chromosomes considerably reduces the probability of stable mAb secretion (Weiss M C, and Green H., 1967). In order to improve growth characteristics and stability of humAb production, heterohybrids between mouse myeloma cells and human lymphocyte (Oestberg L, and Pursch E., 1983) as well as heteromyelomas (Kozbor D, et. al., 1984) are used as the fusion partners.